Method and system for reducing engine exhaust emissions

ABSTRACT

Methods and systems are provided for addressing engine cold-start emissions while an exhaust catalyst is activated. In one example, a method for improving exhaust emissions may include flowing ionized air into an engine exhaust, downstream of an exhaust catalyst, to oxidize exhaust emissions left untreated by the catalyst. The approach reduces the PM load of the exhaust as well as of a downstream particulate matter filter.

FIELD

The present description relates generally to methods and systems forreducing engine cold-start exhaust emissions as well as particulatematter emissions.

BACKGROUND/SUMMARY

Engine out cold-start emissions generated before light-off of an exhaustsystem emission control device (e.g., a catalytic converter) maycontribute a large percentage of the total exhaust emissions. Variousapproaches may be used by engine control systems to expedite theattainment of the catalyst light-off temperature. For example, expensiveelectric catalyst heaters may be used to generate the heat. As anotherexample, various combinations of spark timing retard, valve overlap, andincreased fuel injection may be used to expedite catalyst warming.

In another approach shown by Shimoda in U.S. Pat. No. 7,331,170, aplasma generator is coupled to an emission control device, downstream ofan oxidation catalyst and upstream of a diesel particulate filter.Electricity is discharged by the plasma generator into the exhaust flowto maintain the operating temperature of the particulate filter in atarget operating region.

However, the inventors herein have recognized a potential issue withsuch a system. Since the electrodes of the plasma generator arethemselves exposed to exhaust gas flow, soot and particulates getentrained and accumulated on the electrodes. This can cause leakage ofcurrent, making it difficult for a voltage to be applied across theelectrodes of the plasma generator, and hindering the further generationof plasma. To address this issue, Shimoda requires fuel to beperiodically added upstream of the oxidation catalyst. The resultingheat generated at the oxidation catalyst provides sufficient heat toburn off the soot accumulated on the plasma generator. However, the needto add fuel and periodically regenerate the plasma generator results indegraded fuel economy. In addition, while the generation of plasmaaddresses the temperature requirement of the filter, the temperaturerequirement of other emission control devices coupled in the exhaust mayremain unmet. As a result, exhaust emissions may still be non-compliant.As another example, with the upstream addition of ionized air, theengine may need to run rich to maintain the exhaust catalyst atstoichiometry, thereby degrading fuel economy.

The inventors herein have recognized that cold-start emissions may bebetter addressed by converting the cold-start hydrocarbons using anionized air stream while an emission control device is cold instead of(or in addition to) focusing on expediting light-off of the emissioncontrol device during the cold-start. The use of ionized air may providelower overall emissions that can be implemented in multiple engineconfigurations, including engines operating with different fuels (e.g.,gasoline or diesel) as well as different fuel injection types (e.g.,port or direct injection) with minimal interference with existing enginecold-start controls. In addition, by addressing the exhaust soot usingthe ionized air, the need for particulate filters may be reduced.

Thus, in one example, cold-start engine emissions may be addressed by amethod for an engine comprising: introducing ionized air downstream ofan exhaust catalyst responsive to catalyst temperature. In this way,ionized air may be used to burn off cold-start emissions until anexhaust catalyst is activated.

As one example, during an engine cold-start, while an exhaust catalystwarms up, cold-start emissions may be oxidized as they are generatedusing ionized air. Ionized air may be flowed downstream of the exhaustcatalyst so that exhaust emissions left untreated by the catalyst can beaddressed using the ionized air. For example, ionized airflow may bedelivered so that a threshold fraction of aircharge received downstreamof the exhaust catalyst is provided as ionized air. The flow of ionizedair may be accompanied by spark retard, at a less aggressive clip, toexpedite catalyst heating. In addition, rich engine operation may belimited while ionized air is flowed so as to protect against componentoverheating. Ionized air may continue to be delivered until the exhaustcatalyst is activated, after which time the ionized air flow may beterminated. In addition to adjusting the ionized airflow responsive tocatalyst temperature, the ionized airflow may also be adjusted based onexhaust particulate matter load. For example, ionized air may be flowedduring tip-ins, in anticipation of a rise in exhaust soot load.

In this way, cold start emissions can be addressed as they are generatedwithout needing to expedite catalyst heating using aggressive sparkretard or dedicated catalyst heaters. This allows exhaust emissions tobe reduced without requiring precious metal loading on exhaustcatalysts. This reduces catalyst costs and complexity. By reducing theneed for aggressive spark retard during cold-starts, NVH issuesassociated with aggressive spark retard, such as intake rumble from anear wide open throttle during the spark retard, can be reduced,improving drive quality. By introducing the air downstream of theexhaust catalyst (e.g., an oxidation catalyst or a three-way catalyst),the catalyst can warm up near stoichiometry. This allows the ionized airto oxidize the residual hydrocarbons without generating NOx at theexhaust catalyst. In this way, the introduction of ionized airdownstream of the exhaust catalyst allows emissions reduction benefitsto be achieved during an engine cold-start. It will be appreciated thatin alternate examples, the ionized air may be introduced upstream of theexhaust catalyst. In such an embodiment, in addition to emissionreduction benefits, heating benefits may also be realized. Specifically,with upstream introduction of ionized air, to maintain the three-waycatalyst at stoichiometry, the engine would need to run rich to balancethe ionized air stream. While this may expedite catalyst heating, fueleconomy may be affected.

In hybrid vehicles, the use of ionized air also can provide theopportunity to delay engine pull-ups to a colder catalyst temperature.By also using ionized air to reduce exhaust PM emissions duringcold-starts, as well as other conditions where exhaust soot levels areelevated, particulate matter filter life can be extended. Overall, theimpact on fuel economy is improved while reducing exhaust emissions.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example hybrid electric vehicle system.

FIG. 2 shows an example internal combustion engine configured with anionized air source.

FIG. 3 shows a high level flow chart of a method for reducing enginecold-start emissions using a stream of ionized air.

FIG. 4 shows an example engine cold-start operation using ionized air,according to the present disclosure.

DETAILED DESCRIPTION

Methods and systems are provided for addressing cold-start emissions andparticulate matter emissions from an engine system coupled in a vehicle,such as the system of FIGS. 1-2, using ionized air. An engine controllermay be configured to perform a control routine, such as the exampleroutine of FIG. 3, to stream ionized air into an engine exhaust,downstream of an exhaust oxidation catalyst and upstream of an exhaustparticulate filter, based at least on catalyst temperature. Cold-startemissions that are not oxidized by the oxidation catalyst are oxidizedby the ionized air, reducing exhaust emissions. In addition, duringother conditions when particulate matter (PM) emissions from the engineis higher, ionized air may be used to reduce PM emissions, therebyreducing the reliance on an exhaust particulate filter. Organic matteroxidized by the ionized air may then be expelled through the exhausttailpipe. An example cold-start operation is shown with reference toFIG. 4. In this way, engine exhaust emissions compliance can beimproved.

FIG. 1 depicts a hybrid propulsion system 6 for a vehicle. In thedepicted embodiment, the vehicle is a hybrid electric vehicle (HEV) thatcan derive propulsion power from engine system 8 and/or an on-boardenergy storage device (not shown). In alternate embodiments, propulsionsystem 6 may only derive propulsion power from engine system 8. Enginesystem 8 includes an internal combustion engine 10 having a plurality ofcylinders 30. Fuel may be provided to each cylinder of engine 10 from afuel system (not shown) including one or more fuel tanks, one or morefuel pumps, and injectors 66.

Engine system 8 may include an engine 10 having a plurality of cylinders30. In the present example, engine 10 is a spark-ignition engine of avehicle. Combustion events in each cylinder drive a piston which in turnrotates a crankshaft, as is well known to those of skill in the art.Further, engine 10 may include a plurality of engine valves forcontrolling the intake and exhaust of gases in the plurality ofcylinders.

Engine 10 includes an engine intake 23 and an engine exhaust 25. Engineintake 23 includes a main air intake throttle 62 fluidly coupled to theengine intake manifold 44 via an intake passage 42. Air may enter intakepassage 42 from an air intake system including an air filter 33 incommunication with the vehicle's environment. A position of mainthrottle 62 may be varied by controller 12 via a signal provided to anelectric motor or actuator included with the main throttle 62, aconfiguration that is commonly referred to as electronic throttlecontrol. In this manner, throttle 62 may be operated to vary the intakeair provided to the intake manifold.

In the example embodiment shown in FIG. 1, mass air flow (MAF) sensor 50is coupled in intake passage 42 for providing signals regarding mass airflow in the intake passage to controller 12. In the depicted example,MAF sensor 50 provides a signal regarding mass air flow at the inlet ofintake passage 42, upstream of air filter 33. However, it will beappreciated that the MAF sensors may be coupled elsewhere in the intakesystem or engine system, and further, there may be a plurality of MAFsensors arranged in the intake system or engine system.

A sensor 60 may be coupled to intake manifold 44 for providing a signalregarding manifold air pressure (MAP) and/or manifold vacuum (MANVAC) tocontroller 12. For example, sensor 60 may be a pressure sensor or agauge sensor reading vacuum, and may transmit data as negative vacuum(e.g., pressure) to controller 12. In some examples, additionalpressure/vacuum sensors may be coupled elsewhere in the engine system toprovide signals regarding pressure/vacuum in other areas of the enginesystem to controller 12. These may include, for example, a sensorcoupled to intake passage 42 upstream of the compressor, for providing asignal regarding barometric pressure (BP), a compressor inlet pressure(CIP) sensor arranged upstream of the compressor, etc.

In the depicted embodiment, engine system 8 does not include a boostingdevice and operates with natural aspiration. However, in alternateembodiments, as shown with reference to FIG. 2, engine system 8 may be aboosted engine system including a boosting device in the form of acompressor. The compressor may be, for example, the compressor of aturbocharger, wherein compressor is coupled to and driven by an exhaustturbine via a shaft. Further, the compressor may be, at least in part,driven by an electric motor or the engine crankshaft. In alternateembodiments, the boosting device may be a compressor of a superchargerwherein the compressor is driven only by the electric motor. Whenincluded, the compressor is configured to boost an intake air chargereceived along intake passage 42.

Engine exhaust 25 includes an exhaust manifold 48 leading to an exhaustpassage 35 that routes exhaust gas to the atmosphere. Engine exhaust 25may include one or more emission control devices mounted in aclose-coupled position. The one or more emission control devices mayinclude, for example, oxidation catalyst 70 and particulate matter (PM)filter 72. In the depicted embodiment, oxidation catalyst 70 ispositioned upstream of particulate matter (PM) filter 72. Other emissioncontrol devices coupled to the exhaust may include a three-way catalyst,lean NOx trap, selective reduction catalyst, etc.

When the engine is started under cold ambient conditions, or when theengine is started after a sufficiently long period of being shutdown(e.g., while the vehicle was being propelled via the motor or while thevehicle was shutdown), the exhaust catalyst (e.g., the oxidationcatalyst or catalytic converter) may be at a temperature lower than itsactivation temperature (also known as the light-off temperature). Assuch, engine out cold-start emissions generated before light-off of theexhaust catalytic converter contribute a large percentage of the totalexhaust emissions. To reduce these emission, engine control systems usevarious approaches to expedite heating of the catalyst and attainment ofthe catalyst light-off temperature. For example, expensive electriccatalyst heaters may be used to generate heat locally at the catalyst.As another example, various combinations of spark timing retard, valveoverlap, and increased fuel injection may be used to raise exhausttemperature and thereby expedite catalyst warming. However, suchapproaches can degrade vehicle fuel economy and performance. Theinventors herein have recognized that engine out cold-start emissionscan be addressed without degrading fuel economy using ionized air (alsoreferred to as ionic air). As elaborated herein with reference to FIG.3, ionized air may be introduced into the engine exhaust, downstream ofthe exhaust catalyst so that any exhaust emissions (including organicmatter and particulate matter) that go untreated by the exhaust catalystcan be oxidized by the ionized air. The oxidation improves the qualityof exhaust emissions.

In addition to cold-start conditions, during other engine operatingconditions where the exhaust PM level is expected (or estimated) to behigh, such as during an operator pedal tip-in (e.g., to wide openthrottle), the introduction of ionized air can reduce the soot load ofthe exhaust, thereby improving exhaust emissions and reducing thedependency for soot filtering on a downstream exhaust PM filter. In oneexample, the need for an exhaust PM filter may be obviated, providingcomponent reduction benefits. In still other examples, such as where thePM filter is included, ionized air can also be introduced duringconditions when the PM load of the PM filter necessitates filterregeneration. By introducing ionized air during these conditions, the PMfilter can be regenerated without requiring lean engine operation and atsignificantly lower exhaust temperatures than would otherwise bepossible. Further still, a deceleration fuel shut-off (DFSO) event wouldnot be required to complete the regeneration of the PM filter.

When required, ionized air may be introduced into engine exhaust 25,downstream of oxidation catalyst 70 and upstream of PM filer 72, viaconduit 83 by ionized air system 80. Ionized air system 80 includeselectric air pump 81 and ionizer 82. Specifically, to introduce theionized air, electric air pump 81 may be operated to draw fresh air intoconduit 83 through air filter 34. An output of air pump 81 may beadjusted based on the amount of aircharge expected at exhaust catalyst70 from engine intake 23 so that a threshold portion (e.g., 15%) of thetotal aircharge received downstream of the catalyst can be replaced withionized air from the air pump 81. In addition to operating air pump 81,ionizer 82 may be operated to ionize the air pumped into conduit 83 bypump 81. In one example, the power setting of ionizer 82 may be adjustedso that a threshold (or predefined) portion (e.g., 20%) of the airflowreceived downstream of the exhaust catalyst is ionized. In someexamples, when ionized air is to be flowed into the exhaust, controller12 may coordinate the power setting of ionizer 82, and the flow rate ofair pump 81 with the opening of intake throttle 62 so as to provideionized air at a target ratio (of aircharge) and a target level ofionization.

As such, matter changes its state when energy is supplied to it,specifically, scuds become liquid, and liquids become gaseous. If evenmore energy is supplied to a gas, it is ionized and goes into theenergy-rich plasma state. A plasma (or ionized air) can be created byheating a gas (such as ambient air) or subjecting the gas to a strongelectromagnetic field applied with a generator (such as a laser ormicrowave generator). This decreases or increases the number ofelectrons, creating positive or negative charged particles or ions, andis accompanied by the dissociation of molecular bonds, if present. Thusionizer 82 may use electrostatically charged plates to producepositively or negatively charged gas ions (for instance N₂ ⁻ or O₂ ⁻)that organic and particulate matter sticks to in an effect similar tostatic electricity. In one example, the ionizer may provide an ionizedair stream using a 20,000V electric source. For example, ionized air mayinclude air in which the oxygen content has been given an electricalcharge, which may include a negative charge due to the presence of oneor more extra electrons per oxygen molecule, or a positive charge due tothe presence of less than the normal number of electrons per molecule.It will be appreciated that the ionized air (herein also referred to asionic air or plasma) generated by ionizer 82 may be distinct from ozone(which includes a triple bonded molecule of oxygen). The ionizer (orplasma generator or ionized air source) may use charged electricalsurfaces or needles to generate electrically charged air or gas ions.These ions may attach to particulate matter which are then oxidized orelectrostatically attracted to a charged collector plate. The ionizermay be fan-less or fan-based. In one example, the ionizer may include aplasma source, such as the “Openair” (trademark) Plasma SurfacePreparation System (made by Plasmatreat, 2541 Technology Drive, Elgin,Ill. 60124).

Engine 10 delivers power to a transmission 46 via torque input shaft 18.In one example, transmission 46 is a power-split transmission (ortransaxle) that includes a planetary gearset and one or more rotatinggear elements. Transmission 46 further includes an electric generator 58and an electric motor 56. The electric generator 58 and the electricmotor 56 may also be referred to as electric machines as each mayoperate as either a motor or a generator. Torque is output fromtransmission 46, for propelling vehicle tractions wheels 52, via a powertransfer gearing (not shown), a torque output shaft 19, and adifferential-and-axle assembly (not shown).

Generator 58 is drivably connected to electric motor 56 such that eachof electric generator 58 and electric motor 56 may be operated usingelectric energy from an electrical energy storage device, hereindepicted as battery 54. In some embodiments, an energy conversiondevice, such as an inverter, may be coupled between the battery and themotor to convert the DC output of the battery into an AC output for useby motor. However, in alternate embodiments, the inverter may beconfigured in the electric motor.

Electric motor 56 may be operated in a regenerative mode, that is, as agenerator, to absorb energy from vehicle motion and/or the engine andconvert the absorbed kinetic energy to an energy form suitable forstorage in battery 54. Furthermore, electric motor 56 may be operated asa motor or generator, as required, to augment or absorb torque providedby the engine, such as during a transition of engine 10 betweendifferent combustion modes (e.g., during transitions between a sparkignition mode and a compression ignition mode).

Hybrid propulsion system 6 may be operated in various embodimentsincluding a full hybrid system, wherein the vehicle is driven by onlythe engine and generator cooperatively, or only the electric motor, or acombination. Alternatively, assist or mild hybrid embodiments may alsobe employed, wherein the engine is the primary source of torque and theelectric motor selectively adds torque during specific conditions, suchas during a tip-in event.

Propulsion system 6 may further include control system 14. Controlsystem 14 is shown receiving information from a plurality of sensors 16(various examples of which are described herein and with reference toFIG. 2) and sending control signals to a plurality of actuators 81(various examples of which are described herein and with reference toFIG. 2). As one example, sensors 16 may include exhaust gas sensor 126located upstream of the emission control device, exhaust temperaturesensor 128, exhaust pressure sensor 129, MAP sensor 60, and MAF sensor50. Other sensors such as additional pressure, temperature, air/fuelratio, and composition sensors may be coupled to various locations inthe propulsion system 6. As another example, the actuators may includefuel injector 66, throttle 62, air pump 81, and ionizer 82. The controlsystem 14 may include a controller 12. The controller may receive inputdata from the various sensors, process the input data, and trigger theactuators in response to the processed input data based on instructionor code programmed therein corresponding to one or more routines. Thecontroller 12 receives signals from the various sensors of FIG. 1 (andFIG. 2) and employs the various actuators of FIG. 1 (and FIG. 2) toadjust vehicle operation based on the received signals and instructionsstored on a memory of the controller. It will be appreciated thatvehicle operation may be adjusted by the controller based on actionsperformed by the controller and/or in combination with actions performedby various vehicle and engine actuators acting in concert with thecontroller. An example control routine is described herein with regardto FIG. 3.

FIG. 2 depicts an example embodiment of a combustion chamber or cylinderof engine 10 (of FIG. 1). Engine 10 may receive control parameters froma control system including controller 12 and input from a vehicleoperator 130 via an input device 132. In this example, input device 132includes an accelerator pedal and a pedal position sensor 134 forgenerating a proportional pedal position signal PP. Cylinder (hereinalso “combustion chamber”) 30 of engine 10 may include combustionchamber walls 136 with piston 138 positioned therein. Piston 138 may becoupled to crankshaft 140 so that reciprocating motion of the piston istranslated into rotational motion of the crankshaft. Crankshaft 140 maybe coupled to at least one drive wheel of the passenger vehicle via atransmission system. Further, a starter motor may be coupled tocrankshaft 140 via a flywheel to enable a starting operation of engine10. For example, generator 58 and/or motor 56 of FIG. 1 may be coupledto the crankshaft to provide torque for engine cranking.

Cylinder 30 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 30. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 2 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 62 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 62 may be disposed downstream ofcompressor 174 as shown in FIG. 2, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 30. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 170.Sensor 128 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 170 may bean oxidation calatyst (such as catalyst 70 of FIG. 1), a three waycatalyst (TWC), NOx trap, various other emission control devices, orcombinations thereof. For example, emission control device 170 may beinclude an oxidation catalyst coupled upstream of a gasoline particulatematter filter. A muffler 178 may be included in the exhaust passagedownstream of emission control device 170. As discussed in FIG. 1,during selected conditions, ionized air, generated at ionized air system80, may be flowed into exhaust passage 148, downstream of emissioncontrol device 170 and upstream of muffler 178. Consequently, ionizedair can better interact with exhaust emissions, such as enginecold-start emissions and PM emissions, in the muffler, improving theoxidation of the exhaust emissions with the ionized air. The oxidizedmatter can then be released along the exhaust tailpipe.

In some embodiments, an exhaust gas recirculation passage may beconfigured to recirculate at least a portion of exhaust gas from theexhaust passage to the intake passage. A flow of recirculated exhaustgas (EGR) may be adjusted via an EGR valve coupled to the EGR passage.The EGR passage may be configured to provide low pressure exhaust gasrecirculation (LP-EGR) wherein the exhaust gas is recirculated from theexhaust passage, downstream of turbine 176 to the intake passage,upstream of compressor 174. Alternatively, the EGR passage may beconfigured to provide high pressure exhaust gas recirculation (HP-EGR)wherein the exhaust gas is recirculated from the exhaust passage,upstream of turbine 176 to the intake passage, downstream of compressor174. Further still, the engine may be configured to provide LP-EGR andHP-EGR via respective passages and valves.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. For example, an exhausttemperature may be located downstream of emission control device 170, ormuffler 178, for estimating an exhaust temperature. Alternatively,exhaust temperature may be inferred based on engine operating conditionssuch as speed, load, air-fuel ratio (AFR), spark retard, etc. Further,exhaust temperature may be computed by one or more exhaust gas sensors128. It may be appreciated that the exhaust gas temperature mayalternatively be estimated by any combination of temperature estimationmethods listed herein.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 30 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 30. In some embodiments, eachcylinder of engine 10, including cylinder 30, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 by cam actuation viacam actuation system 151. Similarly, exhaust valve 156 may be controlledby controller 12 via cam actuation system 153. Cam actuation systems 151and 153 may each include one or more cams and may utilize one or more ofcam profile switching (CPS), variable cam timing (VCT), variable valvetiming (VVT) and/or variable valve lift (VVL) systems that may beoperated by controller 12 to vary valve operation. The position ofintake valve 150 and exhaust valve 156 may be determined by valveposition sensors 155 and 157, respectively. In alternative embodiments,the intake and/or exhaust valve may be controlled by electric valveactuation. For example, cylinder 30 may alternatively include an intakevalve controlled via electric valve actuation and an exhaust valvecontrolled via cam actuation including CPS and/or VCT systems. In stillother embodiments, the intake and exhaust valves may be controlled by acommon valve actuator or actuation system, or a variable valve timingactuator or actuation system.

Cylinder 30 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 30 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more injectors for providing a knock or pre-ignition suppressingfluid thereto. In some embodiments, the fluid may be a fuel, wherein theinjector is also referred to as a fuel injector. As a non-limitingexample, cylinder 30 is shown including one fuel injector 166. Fuelinjector 166 is shown coupled directly to cylinder 30 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 168. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 30. While FIG. 2shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing.

Fuel may be delivered to fuel injector 166 from a high pressure fuelsystem 8 including fuel tanks, fuel pumps, and a fuel rail.Alternatively, fuel may be delivered by a single stage fuel pump atlower pressure, in which case the timing of the direct fuel injectionmay be more limited during the compression stroke than if a highpressure fuel system is used. Further, while not shown, the fuel tanksmay have a pressure transducer providing a signal to controller 12. Itwill be appreciated that, in an alternate embodiment, injector 166 maybe a port injector providing fuel into the intake port upstream ofcylinder 30.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Fuel tanks in fuel system 8 may hold fuel with different qualities, suchas different compositions. These differences may include differentalcohol content, different octane, different heat of vaporizations,different fuel blends, and/or combinations thereof etc.

Controller 12 is shown in FIG. 2 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; manifold pressure signal (MAP) from sensor 124,cylinder AFR from EGO sensor 128, and abnormal combustion from a knocksensor. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

It will be appreciated that FIGS. 1-2 show example configurations of avehicle system with relative positioning of the various components. Ifshown directly contacting each other, or directly coupled, then suchelements may be referred to as directly contacting or directly coupled,respectively, at least in one example. Similarly, elements showncontiguous or adjacent to one another may be contiguous or adjacent toeach other, respectively, at least in one example. As an example, enginecomponents laying in face-sharing contact with each other may bereferred to as in face-sharing contact. As another example, elementspositioned apart from each other with only a space there-between and noother components may be referred to as such, in at least one example.

Turning now to FIG. 3, an example method 300 is shown for oxidizingexhaust emissions using ionized air during selected engine operatingconditions. By introducing ionized air downstream of an exhaust catalystresponsive to catalyst temperature, and further based on an exhaust PMload, engine cold-start emissions and PM emissions may be betteraddressed.

At 302, the method includes estimating and/or measuring engine operatingconditions. The conditions estimated may include, for example, enginespeed and load, operator torque demand, pedal position, boost pressure,engine temperature, exhaust temperature, ambient conditions (ambienttemperature, pressure, and humidity, for example), exhaust catalysttemperature, duration (or distance) elapsed since a last engine start,vehicle mode of operation (e.g., whether the vehicle is being operatedin an electric mode, engine mode, or assist mode), etc.

At 304, it may be determined if the exhaust catalyst temperature islower than a threshold, such as lower than a light-off temperature. Assuch, below the threshold temperature, the exhaust catalyst may not befully active and may not be efficient at converting exhaust emissionsbefore their release through the exhaust tailpipe. Thus, if the exhaustcatalyst is not sufficiently hot, the method includes introducingionized air downstream of an exhaust catalyst responsive to catalysttemperature.

Specifically, at 306, the method includes determining the expectedairflow to the engine based on operating conditions. For example, an airmass expected at the exhaust catalyst may be calculated based on theoutput of MAF and/or MAP sensors. In another example, the expectedairflow may be retrieved from a look-up table wherein the airflow isstored as a function of air mass and exhaust backpressure. At 308, themethod includes operating an electric air pump and an ionizer so as toreplace a threshold portion of aircharge received at the catalyst withionized air from the ionizer. For example, a flow rate of the pump maybe adjusted to provide the threshold portion of ionized air. Thethreshold portion may be based on the catalyst temperature relative tothe threshold temperature. For example, the threshold portion may beincreased (by increasing the output of the pump) as the differencebetween the catalyst temperature and the threshold temperatureincreases. In one example, the output of the air pump may be adjusted soas to deliver and an amount of air from the ionizer that is 15% of thetotal air mass flow through the cylinders to the pipe downstream of thecatalyst.

In addition to adjusting the output of the air pump, an output (e.g.,power setting) of the ionizer may also be adjusted so that a thresholdamount (or ratio) of air delivered by the air pump is ionized. Forexample, the power setting of the ionizer may be adjusted so that 20% ofthe air delivered by the air pump is provided as ionized air. One ormore of an amount of ionized air introduced, a rate of introduction ofthe ionized air, and a duration of introduction of the ionized air maybe based on the catalyst temperature relative to the threshold.

At 310, the method includes introducing ionized air generated at the airpump and ionizer to a location downstream of the exhaust catalystresponsive to the catalyst temperature. In addition, organic matter maybe oxidized downstream of the exhaust catalyst using the ionized air. Inone example, the organic matter is oxidized in a mixing chamber (e.g., amuffler) coupled downstream of the exhaust catalyst, the oxidizedorganic matter then released from the mixing chamber into an exhausttailpipe. When mixed in the muffler, a better opportunity is providedfor plasma interaction with the organic matter. Herein, the catalyst isan exhaust oxidation catalyst, and introducing the ionized airresponsive to the catalyst temperature includes initiating introductionof ionized air when the catalyst temperature is below the threshold,continuing to introduce the ionized air until the catalyst temperatureis at the threshold, and discontinuing the introduction of ionized airwhen the catalyst temperature is above the threshold. As will beelaborated herein, the introducing of ionized air may be further basedon an estimated exhaust particulate matter load.

At 312, the method further includes, while introducing the ionized air,limiting rich engine operation to above a threshold air-fuel ratio. Asone example, lambse may be limited to a value of or above 0.90. Inanother example, rich engine operation may be limited to within athreshold degree of richness. By limiting rich engine operation duringconditions when ionized air is introduced into the exhaust,over-temperature conditions in the exhaust are pre-empted. As such, thisaverts exhaust component damage due to overheating.

In some examples, in addition to controlling engine combustion ratiowhile flowing the ionized air, an air-fuel ratio at the exhaust catalystmay be adjusted to be stoichiometric or richer than stoichiometry. Forexample, during an idle warm-up of the catalyst, the air/fuel ratio maybe held just lean of stoichiometry or at stoichiometry. Forpower-enrichment, however, the air/fuel ratio may be adjusted to be richof stoichiometry. The extent or degree of the enrichment may be limitedduring addition of air from the ionizer to avoid exotherms above normallevels in the exhaust pipe when the rich air/fuel mixture mixes with theionizer air.

At 314, the method includes determining if the exhaust temperature (orthe exhaust catalyst temperature) is higher than a threshold, such ashigher than the light-off temperature. As the ionized air oxidizes theexhaust organic matter, heat is generated. If the exhaust is notsufficiently hot, and the exhaust catalyst is still not activated, thenat 316, the method includes continuing to flow ionized air into theengine exhaust downstream of the catalyst and continuing to oxidizecold-start exhaust emissions using the ionized air. If the exhaust issufficiently hot, and the exhaust catalyst is activated, then at 332,the method includes shutting off the air pump and disabling the ionizer,thereby discontinuing delivery of ionized air into the exhaust.

The downstream introduction of ionized air allows the exhaust catalyst(e.g., an oxidation catalyst or a three-way catalyst) to warm up nearstoichiometry while extra air is added at colder temperatures to convertthe residual hydrocarbons into carbon dioxide without generating NOx. Inthis way, the introduction of ionized air downstream of the exhaustcatalyst allows emissions reduction benefits to be achieved during anengine cold-start. It will be appreciated that in alternate examples,the ionized air may be introduced upstream of the exhaust catalyst. Insuch an embodiment, in addition to emission reduction benefits, heatingbenefits may also be realized. Specifically, with upstream introductionof ionized air, to maintain the three-way catalyst at stoichiometry, theengine would need to run rich to balance the ionized air stream. Whilethis may expedite catalyst heating, fuel economy may be affected.

Returning to 304, if the exhaust catalyst is already activated, then at317, the method includes confirming if rich engine operation isrequired. In one example, rich engine operation may be transientlyrequired for component protection, such as when turbine blades (of aturbocharger) or the exhaust catalyst approaches a threshold temperaturethat would degrade component life expectancy. If rich engine operationis required, then the method moves to 332 to maintain the air pump andionizer disabled, thereby disabling delivery of ionized air into theexhaust. This maintains the downstream portion of the exhaust systemwithin the same threshold that the catalyst requires.

If rich engine operation is not required, then at 318, the methodincludes calculating an expected exhaust particulate matter (PM) loadbased on engine operating conditions. In one example, the PM load may bedetermined based on the output of an exhaust soot sensor. In stillanother example, the PM load may be determined based on operator torquedemand and pedal position. For example, during conditions when theoperator torque demand is high, or during an operator pedal tip-in, thePM load of the exhaust may increase.

At 320, the method includes comparing the expected PM load to athreshold load. If the expected PM load of the engine is not higher thanthe threshold load, the method moves to 322 where it may be determinedif regeneration conditions for an exhaust PM filter have been met.Filter regeneration conditions may be considered met if the PM load ofthe exhaust PM filter is higher than a threshold load.

If the expected PM load of the engine is higher than the threshold load,or if PM filter regeneration conditions are considered met, then themethod proceeds to 324 to operate the air pump and the ionizer. Aspreviously discussed, the electric air pump and the ionizer may beoperated to replace a threshold portion (e.g., 15%) of airchargereceived at the PM filter with ionized air from the ionizer. Forexample, a flow rate of the pump may be adjusted to provide thethreshold portion of ionized air. The threshold portion may be based onPM load (or PM filter load) relative to the threshold load, thethreshold portion increased as the difference increases. In addition toadjusting the output of the air pump, an output (e.g., power setting) ofthe ionizer may also be adjusted so that a threshold amount, or ratio ofair delivered by the air pump is ionized, such as 20% of the airdelivered by the air pump is provided as ionized air. One or more of anamount of ionized air introduced, a rate of introduction of the ionizedair, and a duration of introduction of the ionized air may be based onthe PM load (or PM filter load) relative to the threshold.

At 326, the method includes introducing ionized air generated at the airpump and ionizer to a location downstream of the exhaust catalyst andupstream of the PM filter responsive to the PM load. In addition,organic matter may be oxidized downstream of the exhaust catalyst usingthe ionized air. For example, exhaust PMs may be oxidized using theionized air upstream of the PM filter and downstream of the exhaustcatalyst. In one example, the organic matter is oxidized in a mixingchamber (e.g., a muffler) coupled downstream of the exhaust catalyst,and upstream of the PM filter, the oxidized organic matter then releasedfrom the mixing chamber into an exhaust tailpipe. Herein, the ionizedair is introduced responsive to the PM load, the introduction of ionizedair initiated when the PM load is above the threshold load, continuingto introduce the ionized air until the PM load is at the threshold load,and discontinuing the introduction of ionized air when the PM load isbelow the threshold load.

Several advantages are achieved by introducing ionized air based on thePM load. In one example, by better anticipating conditions where exhaustPM load is high, and flowing ionized air during those conditions, theexhaust PMs may be oxidized without the need to accumulate and burn-offthe PMs at a later time. Thus, the need for storing the PMs on a filteris reduced. In other words, the ionized air stream can oxidize the PMsin the exhaust stream as it is produced. In one example, by deliveringionized air during high PM load conditions, the need for a PM filter inthe exhaust can be obviated, providing component reduction benefits(such as reduced cost and improved packaging). In addition, the need forassociated temperature and pressure sensors for filter regenerationcontrol is reduced. Even if a PM filter is present, by flowing ionizedair, the regeneration frequency of the PM filter can be reduced.

Further still, by delivering ionized air during conditions when the PMfilter is loaded and needs regeneration, the filter can be regeneratedat significantly lower exhaust temperatures since the ionized air streamoxidizes soot at much lower temperatures than traditional filterregeneration methods. In addition, a DFSO may not be required toregenerate the filter. By adding the ionized air downstream of theexhaust catalyst, the exhaust catalyst (e.g., a TWC) can beadvantageously used to control air-fuel ratio of gaseous emissions. Bymaintaining the TWC near stoichiometry, emissions of hydrocarbons (HC)and NOx are minimized, allowing the output of the catalyst to be mixedheavily with ionized oxygen to reduce the particulate matter emissions.In this way, the particulate matter load can be reduced without anincrease in NOx emissions, as would occur if the air stream wereintroduced prior to the TWC.

While introducing the ionized air, rich engine operation of the enginemay be limited to above a threshold air-fuel ratio. As one example,lambse may be limited to a value of or above 0.90. By limiting richengine operation during conditions when ionized air is introduced intothe exhaust, over-temperature conditions in the exhaust are pre-empted.As such, this averts exhaust component damage due to overheating.

At 328, the method includes determining if the PM load is lower than thethreshold load or if the filter has been regenerated. If not, then at330, the method continues to flow ionized air into the engine exhaust.Else, at 332, the air pump and ionizer may be shut off, therebydisabling delivery of ionized air into the exhaust.

In this way, ionized air can be advantageously used during engineoperation to expedite exhaust heating, catalyst activation, and controlexhaust PM issues. By reducing the need for aggressive spark retardduring a cold-start, NVH can be improved by reducing the near wide openthrottle intake rumble that comes from use of aggressive spark retard.In addition, precious metal loading on the exhaust catalyst can bereduced, lowering catalyst costs.

In one example embodiment, a method for a hybrid vehicle systemcomprises: in response to one or more of an exhaust catalyst temperaturebeing below an activation threshold, and an exhaust particulate matterload being higher than a threshold load, operating an ionizer tointroduce ionized air downstream of the exhaust catalyst. The exhaustparticulate matter load may be one of an estimated exhaust particulatematter load estimated by a soot sensor, an expected exhaust particulatematter load inferred based on engine operating conditions, and a sootload of a particulate filter coupled downstream of the exhaust catalyst.The method may further comprise, continuing operation of the ionizeruntil the exhaust catalyst temperature is at or above the activationthreshold, or the exhaust particulate matter load is below the thresholdload. Herein, the operating includes, enabling the ionizer and adjustingan output of an electric air pump coupled to the ionizer so as to add athreshold fraction of aircharge received downstream of the exhaustcatalyst with ionized air.

The method may further comprise, while introducing the ionized air,limiting an engine combustion air-fuel ratio to be at or above athreshold air-fuel ratio, the threshold air-fuel ratio based one of aduration and an amount or ionized air introduced downstream of thecatalyst. In addition, in response to a request for rich engineoperation for engine component protection, the method may includedisabling operation of the ionizer. Further still, the method mayinclude, oxidizing exhaust organic matter, including exhaust particulatematter, in a mixing chamber coupled downstream of the exhaust catalyst,and releasing the oxidized organic matter and heat from the mixingchamber into an exhaust tailpipe.

It will be appreciated that in hybrid electric vehicles, by usingionized air to address cold-start emissions, an opportunity is providedto allow pull-downs to be longer by waiting until a colder catalysttemperature to pull-up the engine to heat the catalyst. In one exampleembodiment, a hybrid vehicle system comprises an engine including anintake and an exhaust, the exhaust including an oxidation catalyst; anelectric air pump for flowing air into an ionizer; an ionizer forionizing air into ionic air; an electric motor; vehicle wheels propelledvia one or more of the engine and the electric motor; and a controller.The controller may be configured with computer-readable instructionsstored on non-transitory memory for: during a first engine cold-start ofa drive cycle, discontinuing vehicle propulsion via the motor whileoperating the engine with ignition timing retard to raise a temperatureof the catalyst above a threshold temperature. Then, during a second,subsequent engine cold-start of the drive cycle, the controller maycontinue vehicle propulsion via the motor while the catalyst cools to alower temperature. Then, while operating the engine, the controller mayflow ionized air into the engine exhaust, downstream of the exhaustcatalyst to reduce HC emissions at the tailpipe until the temperature ofthe exhaust catalyst is above the threshold temperature. In this way,emissions are maintained at low level not possible using spark retardalone on a cold catalyst.

The first engine cold-start of the drive cycle may be performedresponsive to an initial drop in exhaust catalyst temperature during thevehicle propulsion via the motor, while the second engine cold-start ofthe drive cycle may be performed responsive to a subsequent drop inexhaust catalyst temperature while the vehicle is propelled via themotor. A drop in catalyst temperature during the first engine cold-startof the drive cycle may be to a lower temperature than the drop incatalyst temperature during the second engine cold-start of the drivecycle. Further, a particulate matter load of exhaust gas during thefirst engine cold-start of the drive cycle may be higher than theparticulate matter load of exhaust gas during the second enginecold-start of the drive cycle. The controller may include furtherinstructions for flowing ionized air into the engine exhaust byoperating the ionizer and adjusting an output of the electric air pumpbased on a difference between the temperature of the exhaust catalystand the threshold temperature.

Now turning to FIG. 4, map 400 depicts an example use of ionized air inan engine exhaust responsive to catalyst temperature and particulatematter load. Map 400 depicts the temperature of an exhaust catalyst atplot 402, an exhaust PM load at plot 404, flow of ionized air at plot406, an operator pedal position at plot 408, engine fuel injection atplot 410, exhaust air-fuel ratio at plot 412, vehicle speed at plot 414,and spark timing retard (from MBT) at plot 416. In the present example,the vehicle is a hybrid vehicle that can be propelled via an engine, amotor, or both.

Prior to t1, the vehicle is operating in an electric mode with thewheels being propelled via motor torque only. No engine combustionoccurs at this time, and no engine torque is generated or delivered tothe wheels. At t1, the operator may tip-in to request a higher vehiclespeed. To deliver to demanded torque, the engine may need to be started.Accordingly, fuel and spark are resumed in the engine to generate enginetorque. However, at this time, the catalyst temperature is below itsactivation temperature. To reduce cold-start emissions associated withthe inactive catalyst, the engine is operated with some spark retard. Inaddition, ionized air is flowed into the engine exhaust passage,downstream of the exhaust catalyst. In the present example, ionized airis flowed at a predefined rate, however, it will be appreciated that inalternate examples, the flow of ionized air may also be varied. Byproviding some spark retard from MBT, the exhaust temperature, andthereby the exhaust catalyst temperature, may be raised. By flowingionized air concurrently, while the catalyst gets activated, untreatedhydrocarbons that are not converted by the catalyst can be oxidized bythe ionized air, reducing exhaust emissions. As such, if ionized airwere not introduced during the cold-start, exhaust PM emissions may havebeen significantly higher, as shown by dashed segment 401. It will alsobe appreciated that by introducing ionized air during the cold-start toaddress the exhaust emissions, spark retard can be used lessaggressively to expedite catalyst heating. In one example, between t1and t2, spark timing may be retarded from MBT by a smaller amount and/ormay be retarded for a shorter duration as compared to the spark retardusage shown at plot 416.

At t2, the catalyst may be sufficiently warm, and therefore furtherdelivery of ionized air may be terminated. In addition, spark timing maybe returned to MBT and no further spark retard may be applied forcatalyst heating purposes. Between t2 and t3, the vehicle may continueto be operated with at least some engine torque. At t3, the operator maytip-in again. For example, the operator may transiently tip-in to wideopen throttle. As such, during the tip-in, exhaust PM emissions mayrise. To address this PM load, at t3, while the operator tips-in andexhaust soot is produced, the delivery of ionized air to the engineexhaust, downstream of the exhaust catalyst, is reinitiated. By flowingionized air during conditions when exhaust PM levels rise, the soot canbe oxidized as it is generated, averting exhaust emission degradation.Specifically, by providing ionized air when soot levels are expected tobe higher, the resulting exhaust PM emissions may be rendered lower thanwould have otherwise been possible. For example, in the absence ofionized air delivery, exhaust PM emissions may have been higher, asshown by dashed segment 403.

At t4, operator torque demand may drop and may be at a level that can beprovided via motor torque only. Accordingly, the engine may be shut downand the vehicle may be propelled via the motor only.

Between t4 and t5, as the vehicle operates with motor torque only, thecatalyst temperature starts to drop. At t5, the catalyst temperature maybe low enough to where exhaust PMs may be generated if the engine wereoperated (shown by dashed segment 405). Accordingly, at t5, ionized airmay be delivered to the exhaust downstream of the exhaust catalyst,reducing exhaust PM emissions. At t6, the catalyst temperature may dropfurther and may now require the engine to pulled-up for catalystheating. Accordingly, at t6, the engine is restarted and operated withspark retard to expedite catalyst heating. Herein, the engine pull-up isdelayed until t6, at a cooler catalyst temperature than would haveotherwise been possible. Specifically, in the absence of ionized airdelivery, the engine may need to be pulled up at t5.

In another representation, over a given drive cycle, responsive to afirst drop in exhaust catalyst temperature while propelling a hybridvehicle via a motor, a controller may immediately transition tooperating the engine with ignition timing retard and maintain engineoperation at least until a temperature of an exhaust catalyst is above athreshold temperature. In comparison, responsive to a second, subsequentdrop in exhaust catalyst temperature while propelling the vehicle viathe motor, the controller may maintain motor operation while flowingionized air into the engine exhaust, downstream of the exhaust catalystuntil the temperature of the exhaust catalyst is above the thresholdtemperature.

In this way, each of exhaust particulate matter emissions and enginecold-start emissions can be addressed without needing to rely on fuelinefficient methods to expedite catalyst heating. The technical effectof flowing ionized air into an engine exhaust, downstream of an exhaustcatalyst, is that cold-start emissions and exhaust PMs can be oxidizedas they are generated, improving exhaust emissions. This not onlyreduces the need for exhaust particulate filters, but also the costs andcontrols involved with filter regeneration, such as the need for leanengine operation, additional temperature and pressure sensors, as wellas the need to regenerate exclusively during DFSO operations. Inaddition, packaging is facilitated. Thermal issues related to filterover-activation are also reduced due to lower levels of sootaccumulation. Further, cold start frequency can be reduced and thereforeemissions can be addressed as they are generated without needing toexpedite catalyst heating using fuel inefficient methods, such asaggressive spark retard. This also reduces the need for precious metalloading on an exhaust catalyst, reducing catalyst costs. Also, theaddition of the ionized air downstream of the exhaust catalyst enablesthe catalyst to be operated near stoichiometry, enabling PM emissions tobe reduced without causing an increase in NOx emissions. Overall, theimpact on fuel economy is improved while reducing exhaust emissions.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for an engine, comprising: introducing ionized airdownstream of an exhaust catalyst responsive to catalyst temperature. 2.The method of claim 1, further comprising, oxidizing organic matterdownstream of the exhaust catalyst using the ionized air.
 3. The methodof claim 2, wherein the catalyst is an exhaust oxidation catalyst, andwherein the introducing includes initiating introduction of ionized airwhen a catalyst temperature is below a threshold, continuing tointroduce the ionized air until the catalyst temperature is at thethreshold, and discontinuing the introduction of ionized air when thecatalyst temperature is above the threshold.
 4. The method of claim 3,wherein the introducing includes operating an electric air pump and anionizer so as to add a threshold portion of aircharge received at thecatalyst with ionized air, the threshold portion based on the catalysttemperature relative to the threshold.
 5. The method of claim 3, furthercomprising, adjusting one or more of an amount of ionized airintroduced, a rate of introduction of the ionized air, and a duration ofintroduction of the ionized air based on the catalyst temperaturerelative to the threshold.
 6. The method of claim 2, wherein theoxidizing includes oxidizing organic matter in a mixing chamber coupleddownstream of the exhaust catalyst, and releasing the oxidized organicmatter from the mixing chamber into an exhaust tailpipe.
 7. The methodof claim 1, wherein the introducing of ionized air is further based onan estimated exhaust particulate matter load.
 8. The method of claim 1,further comprising, while introducing the ionized air, limiting richengine operation to above a threshold air-fuel ratio.
 9. A method for ahybrid vehicle system, comprising: in response to one or more of anexhaust catalyst temperature being below an activation threshold, and anexhaust particulate matter load being higher than a threshold load,operating an ionizer to introduce ionized air downstream of the exhaustcatalyst.
 10. The method of claim 9, wherein the exhaust particulatematter load is one of an estimated exhaust particulate matter loadestimated by a soot sensor, an expected exhaust particulate matter loadinferred based on engine operating conditions, and a soot load of aparticulate filter coupled downstream of the exhaust catalyst.
 11. Themethod of claim 9, further comprising, continuing operation of theionizer until the exhaust catalyst temperature is at or above theactivation threshold, or the exhaust particulate matter load is belowthe threshold load.
 12. The method of claim 9, wherein the operatingincludes, enabling the ionizer and adjusting an output of an electricair pump coupled to the ionizer so as to add a threshold fraction ofaircharge received downstream of the exhaust catalyst with ionized air.13. The method of claim 9, further comprising, while introducing theionized air, limiting an engine combustion air-fuel ratio to be at orabove a threshold air-fuel ratio, the threshold air-fuel ratio based oneof a duration and an amount or ionized air introduced downstream of thecatalyst.
 14. The method of claim 9, further comprising, in response toa request for rich engine operation for engine component protection,disabling operation of the ionizer.
 15. The method of claim 9, furthercomprising, oxidizing exhaust organic matter, including exhaustparticulate matter, in a mixing chamber coupled downstream of theexhaust catalyst, and releasing the oxidized organic matter and heatfrom the mixing chamber into an exhaust tailpipe.
 16. A hybrid vehiclesystem, comprising: an engine including an intake and an exhaust, theexhaust including an oxidation catalyst; an electric air pump forflowing air into an ionizer; an ionizer for ionizing air into ionic air;an electric motor; vehicle wheels propelled via one or more of theengine and the electric motor; and a controller with computer-readableinstructions stored on non-transitory memory for: during a first enginecold-start of a drive cycle, discontinuing vehicle propulsion via themotor while operating the engine with ignition timing retard to raise atemperature of the catalyst above a threshold temperature; and during asecond, subsequent engine cold-start of the drive cycle, continuingvehicle propulsion via the motor while flowing ionized air into theengine exhaust, downstream of the exhaust catalyst, while operating theengine, until the temperature of the exhaust catalyst is above thethreshold temperature.
 17. The system of claim 16, wherein the firstengine cold-start of the drive cycle is responsive to an initial drop inexhaust catalyst temperature during the vehicle propulsion via themotor, and wherein the second engine cold-start of the drive cycle isresponsive to a subsequent drop in exhaust catalyst temperature whilethe vehicle is propelled via the motor.
 18. The system of claim 16,wherein a drop in catalyst temperature during the first enginecold-start of the drive cycle is to a lower temperature than the drop incatalyst temperature during the second engine cold-start of the drivecycle.
 19. The system of claim 16, wherein a particulate matter load ofexhaust gas during the first engine cold-start of the drive cycle is ahigher than the particulate matter load of exhaust gas during the secondengine cold-start of the drive cycle.
 20. The system of claim 16,wherein the controller includes instructions for flowing ionized airinto the engine exhaust by operating the ionizer and adjusting an outputof the electric air pump based on a difference between the temperatureof the exhaust catalyst and the threshold temperature.